1. Field of the Invention
The present invention relates to a thin-film piezoelectric material element which has a piezoelectric material and electrodes having thin-film like shape and method of manufacturing the same, head gimbal assembly, hard disk drive, ink jet head, variable focus lens and sensor having the thin-film piezoelectric material element.
2. Related Background Art
A hard disk drive has a large recording capacity and is used as the heart of a storage device. The hard disk drive records and reproduces data to/from a hard disk (recording medium) by a thin-film magnetic head. A part, which the thin-film magnetic head is formed, is called as a head slider, and a part, which the head slider is mounted on the edge part, is a head gimbal assembly (will also be referred to as HGA).
Further, recording and reproducing of data to/from the recording medium is performed by flying the head slider from a surface of the recording medium while rotating the recording medium, in the hard disk drive.
On the other hand, it has become difficult to control a position of the thin-film magnetic head accurately by control with only a voice coil motor (VCM), because heightening a recording density of the recording medium has developed in company with increase of a capacity of the hard disk drive. Therefore formerly, a technology, which an actuator having supplementary function (a supplementary actuator) is mounted on the HGA in addition to a main actuator with the VCM, and the supplementary actuator controls a minute position that is not able to be controlled by the VCM, is known,
A technology, which the main actuator and the supplementary actuator control the position of the thin-film magnetic head, is also called two stage actuator system (dual-stage system).
In the two stage actuator system, the main actuator makes drive arms rotate to decide a position of the head slider on a specific track of the recording medium. Further, the supplementary actuator adjusts the position of the head slider minutely so that the position of the thin-film magnetic head may become an optimum position.
A micro actuator using a thin-film piezoelectric material element is known formerly as the supplementary actuator. The thin-film piezoelectric material element has a piezoelectric material and a pair of electrodes formed to sandwich the piezoelectric material, and each of them is formed to be a thin-film shape.
Further, for example, as disclosed in the JP 2003-101095 (referred to also as Patent Document 1), the thin-film piezoelectric material element having two layers structure, which two piezoelectric laminated materials including the piezoelectric material are overlaid, is known as the conventional thin-film piezoelectric material element.
The piezoelectric laminated material has a structure which the piezoelectric material and electrode films are formed on a substrate, and it sometimes cause a displacement (also referred to as crooked displacement) along the direction where it is not intended. Further, there is a problem which the piezoelectric laminated material has been curved even a condition which a voltage is not applied to, because stress of each film constituting the piezoelectric laminated material is not equal, or is not symmetrical along to the thickness direction. Accordingly, there is a problem which the piezoelectric laminated material is not able to be mounted on a desired position of the HGA, and the piezoelectric laminated material is broken when it is mounted on the HGA. However, if each piezoelectric laminated material is laminated so that the electrode films, of one pair of electrode films, connected to the outside, oppose each other, crooked displacement caused by each piezoelectric laminated material are canceled each other. Therefore, an effect, which crooked displacement in the whole thin-film piezoelectric material element is suppressed, is obtained. Further an effect, which the thin-film piezoelectric material element is mounted easily on the HGA without broken, is obtained due to canceling curve of each piezoelectric laminated material.
However, on the other hand, it is necessary for the thin-film piezoelectric material element having two layers structure to pile up the piezoelectric laminated material with adhesive. Therefore, there is a problem which both improvement of the mass production capability and lowering of the manufacturing cost are difficult in the thin-film piezoelectric material element having two layers structure.
Hence, conventional method, which a stress occurred between the piezoelectric material and the substrate is released at a manufacturing stage, thereby the crooked displacement and curve (or bowing) are able to be suppressed even the piezoelectric laminated material having single layer, is provided as the method of manufacturing the thin-film piezoelectric material element (see for example, P4897767 (referred to also as Patent Document 2)).
On the other hand, the piezoelectric laminated material having single layer is not able to avoid a generation of stress inside of the piezoelectric laminated material, because it needs a piling up of plurality of thin-films. Therefore, the piezoelectric material elements disclosed in the JP 2012-76387 (referred to also as Patent Document 3), JPH 11-87791 (referred to also as Patent Document 4) are known. The piezoelectric material elements, which electrode of one side has two layers structure and the outside of them is formed with material having small compressing stress than the inside one, so stress of the electrode entirely is relaxed, is disclosed in the Patent Document 3. Further, the piezoelectric material elements, having a structure which two piezoelectric materials are piled up sandwiching a relaxing layer, and two electrodes are arranged both side of the two piezoelectric materials, is disclosed in the Patent Document 4.